Patent Document 1 discloses a hydraulic brake system including (a) a master cylinder including a pressurizing piston coupled to a brake pedal and designed to generate a hydraulic pressure related to a brake operating force, in a front chamber located in front of the pressurizing piston, (b) a master-cylinder-pressure sensor for detecting a hydraulic pressure in the front chamber, (c) a foot power sensor for detecting a foot power applied to the brake pedal, and (d) a liquid leakage detector configured to detect that there is a liquid leakage from a hydraulic pipe line for coupling a pressure chamber and a brake cylinder to each other, in a case where a value detected by the master-cylinder-pressure sensor is small when compared with a hydraulic pressure in the front chamber which is estimated based on a value detected by the foot power sensor.
Patent Document 2 discloses a hydraulic brake system including (1) a power hydraulic pressure source designed to produce a hydraulic pressure by a supply of electric power, (ii) a pressure-buildup linear valve provided between the power hydraulic pressure source and a brake cylinder, (iii) a pressure-reduction linear valve provided between the brake cylinder and a reservoir, and (iv) a liquid-leakage detection device designed to detect presence or absence of the liquid leakage from each of the pressure-buildup linear valve and the pressure-reduction linear valve based on a change in a hydraulic pressure in the brake cylinder in a state in which currents supplied to solenoids of the pressure-buildup linear valve and the pressure-reduction linear valve are controlled such that the pressure-buildup linear valve and the pressure-reduction linear valve are in their respective closed states.
Patent Document 3 discloses a hydraulic brake system including: a master cylinder; a brake cylinder coupled to a pressure chamber located in front of a pressurizing piston; and a master-cylinder-pressure sensor for detecting a hydraulic pressure in the pressure chamber of the master cylinder.